Method of producing a reduced metal, and traveling hearth furnace for producing same

ABSTRACT

A traveling hearth for producing reduced metal by charging and stacking a raw material containing a metal-containing material and a solid-reducing material on a horizontally moving hearth, arranged for disposing a solid-reducing material layer on the hearth, forming concave portions at the solid-reducing material surface, stacking the raw material on the surface of the solid-reducing material layer, reducing the raw material by at least once heating and melting the material on the hearth to separate metal and gangue and ash ingredients, and discharging metal from the hearth.

RELATED APPLICATION

This is a divisional application out of U.S. application Ser. No.09/280,386 now U.S. Pat. No. 6,126,718 filed Mar. 29, 1999, which inturn is based upon Japanese Applications No. 11-026739 filed Feb. 3,1999 and No. 10-141227 filed May 22, 1998.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention concerns apparatus for of producing reduced and purifiedmetal from a metal-containing raw and at least partially oxidizedmaterial. More particularly, this invention relates to an apparatuscapable of a novel technique of charging and stacking metal-containingmaterial on a hearth that is moving in a furnace, for heating andreducing the metal-containing material by heating during movement of thehearth. The apparatus at this invention continuously produces reducedmetal of high quality from a traveling hearth furnace, with unexpectedeconomy and efficiency.

2. Description of the Related Art

Steels are generally produced either by a converter or an electricfurnace. Electric furnace steels are produced by heating and meltingscrap or reduced iron by using electrical energy, followed optionally byrefining the same. However, since the supply of scrap has become scarceand the demand for high quality steels has increased more and more inrecent years, reduced iron has been used more than scrap.

As one reduced iron process, the method of the traveling hearth furnacehas been known. One example is shown in Japanese Patent UnexaminedPublication Sho 63-108188. Iron ores and solid reducing materials arecharged onto a hearth moving in a horizontal direction, and the ironores are heated and reduced by radiant heat transfer from above, toproduce reduced iron. As shown in FIG. 1 of that Japanese publication,charged raw material can be heated during horizontal movement of thehearth. The hearth is usually adapted to rotate as shown, and the hearthfurnace is usually referred to as a rotary hearth furnace.

As shown in FIG. 1(a) of the drawings of this application, the rotaryhearth furnace has an annular hearth body partitioned into a preheatingzone 10 a, a reducing zone 10 b and a cooling zone 1 d, located alongthe supply side to the discharge side of the furnace. An annular hearth11 is supported in the furnace body so as to move rotationally.

As shown in FIG. 1(b) of the drawings, a raw material 2 comprising amixture, for example, of iron ore and solid reducing material, ischarged. Pellets having incorporated carbonaceous material arepreferably used. The hearth 11 has refractory applied on the surfacethereof, or granular refractory may be stacked. A burner 13 is disposedin an upper portion of the furnace body, and metal-containing oxidessuch as iron ores stacked on the hearth 11 are reduced by heating in thepresence of the reducing material into reduced iron by using the burner13 as a heat source.

In FIG. 1(a) of the drawings, the number 14 represents a feed device forcharging the raw material onto the hearth, and 15 denotes a dischargedevice for the reduced product.

In the usual operation of a traveling hearth furnace, the atmospherictemperature in the furnace body 10 is preferably about 1300° C. Thereduced product after completion of the reducing treatment is cooled atthe cooling zone 10 d (FIG. 1(a)) on the rotating hearth 11, forpreventing reoxidation and facilitating discharge from the furnace.

In the operation of the traveling hearth of Japanese Patent UnexaminedPublication Sho 63-108188), in conducting the reducing reaction betweenthe iron ore and the solid reducing material, improved productivity isintended to be obtained by decreasing the thickness of the raw materiallayer and increasing the moving speed of the hearth. However, seriousproblems arise, as will be detailed hereinafter.

The usual metal-containing materials, for example iron ores, contain agreat amount of a gangue ingredient, although this varies depending onthe place of production. Coal, coal char and coke, which are typicalsolid reducing materials, contain a substantial ash ingredient.Accordingly, if the reduced iron is produced only by a reductionreaction, it is inevitable that a great amount of gangue remains in thereduced iron product. Further, ashes adhere to the reducing material andcontaminate the reduced iron.

If reduced iron containing a great amount of gangue and ash are thencharged into an electric furnace, the amount of calcium oxide thatcontrols the slag CaO/SiO ratio for dephosphorization anddesulfurization is increased. This seriously increases the cost, as wellas the amount of electric power used, along with increase of heat energyrequired for formation of slag.

Further, reduced iron obtained only by a reducing reaction usuallycontains a substantial number of pores, making the iron highlyreoxidizable when stored in atmospheric air. This deteriorates thequality of the product and even suffers from the danger of fire causedby generation of heat upon reoxidation. Further, since the porousreduced iron has a low apparent density due to the presence of pores, itfloats on slag when used in an electric furnace, sometimes making itdifficult to achieve smooth melting and refining. In addition, if thesize of the reduced iron product is too great, it takes a long time tomelt it in the electric furnace, thereby slowing the productivity of theelectric furnace. Accordingly, it is indispensable to decrease the sizeof the reduced iron.

Accordingly it has been demanded, in the operation of traveling hearthfurnaces, to use iron ores of high quality with the gangue percentage aslow as possible, and to use a reducing material having an ash content aslow as possible. However, sources of pure iron ores or high qualitycoals are very scarce and expensive. In fact, materials of low qualityhave to be used whenever possible.

In view of the background as described above, there is a great need foreffectively separating a metallic ingredient such as Fe from the usualgangue ingredient and recovering a metallic ingredient, and to do thisin the operation of a traveling hearth furnace.

OBJECTS OF THE INVENTION

An important object of the present invention is to produce a highquality reduced metal of an appropriate size, with low gangue and ashcontents, and having a small amount of pores.

Another object of the present invention is to establish a technique foreasily producing a reduced metal of high quality at a reduced costwithout increasing the use of refractory or electric energy.

A further object of the present invention is to produce a reduced metalhaving excellent storability and convenience in handling.

It is another object to separate a metal ingredient and a gangueingredient completely, and to separate reduced iron and gangue and theash, by melting as a part of a reducing operation, with molten metal andmolten slag formed in a reducing operation.

BRIEF DESCRIPTION OF THE INVENTION

For solving the foregoing problems in the prior art, there is providedin the present invention, apparatus for of producing a reduced metalfrom a metal-containing reducible material, by charging a raw materialcontaining the metal-containing material and a solid reducing materialon a horizontally moving hearth of a traveling hearth furnace, andheating the raw material during movement of the hearth in the furnace toobtain a reduced metal, wherein the raw material is charged and stackedon the hearth, and heated to a molten condition at least once.

Another feature of the invention comprises apparatus for forming a solidreducing material layer on the hearth, charging and stacking the rawmaterial in the form of separate stacks on the solid reducing materiallayer, reducing the material by heating, and melting the product atleast once.

Still another feature of the present invention resides in apparatus formelting the reduced material at least once to make molten metal andmolten slag, and cooling the thus obtained molten metal and molten slagto make a plurality of individual solid metal and solid slag objectswhile arranging them in a generally spotwise configuration, separatedfrom each other on the surface of the reducing material layer.

Another feature of the invention resides in apparatus for stacking theraw reducible material on top of the solid reducing material layer thatlies on the hearth surface, so as to form a plurality of convex andconcave portions on the surface of the solid reducing material layer,subsequently reducing the reducible material by heating, and melting thesame at least once, and then cooling the thus obtained molten bodies toform a plurality of solid objects while keeping them in a spotwisearrangement, spaced apart from each other on the surface of the reducingmaterial layer.

Yet another feature of the present invention resides in apparatus forforming a solid reducing material layer on the hearth, charging andstacking the raw metallic material on top of the solid reducing materiallayer, then forming a plurality of concave cups or cup-like portions onthe surface of the solid reducing material layer, then charging andstacking the raw material on top of the solid reducing material layer,reducing the same by heating, melting the raw reducible material atleast once, and cooling the thus obtained molten contents in the cupswhile keeping them in a scattered, spotwise arrangement in the cups ofthe reducing material layer.

In operating the apparatus of the present invention, a flux ispreferably introduced into or dispersed on the surface of the solidreducing material layer covering the hearth.

In operating the apparatus of the present invention, a further layerwhich is not softened nor melted under the existing heating conditionsis preferably disposed in the solid reducing material layer covering thesurface of the hearth, at least on the surface of the hearth.

In operating the apparatus of the present invention, the thickness ofthe layer of the solid reducing material covering the hearth ispreferably about 5 mm or more, preferably about 10 mm or more.

In the present invention, different kinds of raw materials may belaminated to form a stacked layer when the raw material is charged andstacked on the solid reducing material layer.

In the present invention, agglomerates of metals and slags resultingfrom the process may be sieved from the reduced products, and powderymaterials passing through the sieve may be entirely or partially mixedwith further raw materials for reuse.

In the present invention, the raw material preferably contains Zn and/orPb in the metal-containing material, for reasons further explainedhereinafter.

In the present invention, a reducing atmosphere is preferably formed andmaintained in the traveling hearth furnace, at least in the region wherethe raw material is melted.

In the present invention, it is preferred that materials other than thesolid reducing material in the raw material may be preheated outside ofthe traveling hearth furnace, mixed with the solid reducing material andthen charged into the traveling hearth furnace.

Raw metallic reducible materials used in the operation of the apparatusof the present invention may include iron ores, Cr ores, Ni ores, ironsand, reduced iron powder, blast furnace dusts, steel-making dusts,stainless refining dusts and iron making sludges containing metals suchas iron, Ni and Cr. Further, coal char, coke, non-coking coal andanthracite can be used as the solid reducing material.

Each of the metal-containing materials and the solid reducing materialsmay be used alone or as a mixture of two or more materials. Themetal-containing materials and the solid reducing materials are mixedand used as raw materials to be charged.

The weight ratio of the solid reducing material in the raw material ispreferably about 50% or less. Reduction of common metal-containingmaterial can be sufficiently achieved if the solid reducing material ismixed into the raw material up to about 50 weight %. Further, reducedproducts often become small in the size because of hindrance ofgathering of the metal and the slag in case more reducing material thannecessary is mixed into the raw material. Therefore, the weight ratio ofthe solid reducing material in the raw material is preferably about 30%or less in case the produced metals are expected to be within thedesired size limitations.

An auxiliary raw material may be added to the reducible raw material forfacilitating melting of the reduced metal and ash ingredient duringmelting. Such auxiliary raw material may be steel making slag,limestone, fluorspar, serpentine, dolomite and the like.

The reducible raw material can desirably be used in the form of a powderof about 8 mm or less or briquettes or pellets previously agglomeratedwith the powder, but other forms of the material may be used.

The solid reducing material layer is preferably laid entirely on thehearth; it may be the same reducing material as that mixed with thereducible raw material, or a different solid reducing materialcomposition.

The grain size of the solid reducing material may be controlled to sucha size that the molten material preferably does not penetrate the solidreducing material layer and does not penetrate down to the hearthrefractory upon melting of the raw material. For this purpose, a powderof about 8 mm or less can be used. More preferably, this may becontrolled to about 5 mm or less.

The raw material charged on the solid reducing material layer formed onthe hearth is reduced by heating and, with further heating, is melted toform metal and slag. In this process, the raw material is preferablycharged by being uniformly stacked substantially on the entire surfaceof the hearth, in the interest of heat transmission efficiency.

When the raw material is heated and melted and separated into metal andslag, the metal and the slag respectively coagulate and are dispersedspotwise on the surface of the solid reducing material layer because ofsurface tensions of their own. For reliably attaining such spotwisedispersion of the metal and the slag, the spotwise presence and separatecontainment of the metal and the slag are preferably ensured byphysically forming concave cup-like depressions on the upper surface ofthe solid reducing material layer, and gathering the metal and the slagin the concave cup-like depressions. Upon cooling, separate bodies ofsolid metal and solid slag remain, and can be collected separately.

The amount of the reducible raw material to be charged in the hearth isvariable, depending upon many factors.

Usually, upon melting, the volume of the molten metal and the slagshrinks to about 10-60 vol % based on the original volume of thereducible raw material. Accordingly, the raw material can be charged inan amount up to about ten times the entire volume of the inner spaces inthe concave cup-like portions desired to be formed on the upper surfaceof the solid reducing material layer. Desirably, the amount of rawmaterial charged into the furnace is limited to such an extent that themolten metal and slag substantially fill the insides of the concavecup-like portions when the concave portions are formed on the surface ofthe solid reducing material layer.

Further, according to the present invention, the traveling hearthfurnace comprises a horizontally moving hearth, an enclosure disposedabove and covering the hearth, a charging device for charging a materialto be charged containing a metal-containing material and a solidreducing material on the hearth, a heating means for heating thematerial on the hearth, a cooling means for cooling reduced product andslag, and a discharging means for discharging the cooled reduced metalproduct and the slag. The furnace preferably includes a preheating zonefor preheating the material to be charged, a reducing zone for reducingthe material to be charged, a melting zone for melting and reducing thematerial, and a cooling zone for cooling the molten reduced product andthe slag.

Particularly, it is preferred to form the upper surface of the hearthand the inner lateral surface of the furnace body with refractory toprovide a structure capable of withstanding a high temperature in thefurnace.

A heating means may be disposed in the furnace. For example, a burnerfor fuel gas or liquid fuel may be disposed in the enclosure above thehearth in the furnace to heat directly the material to be processed,using heat of combustion or heat transferred from the inner wall of thefurnace body to heat the charged material by radiation. As analternative method, heating may be applied, partially or entirely, by anelectric heater disposed adjacent to the hearth or the furnace wall.

The preheating zone, the reducing zone, the melting zone and the coolingzone may be established by properly controlling the temperature in thefurnace without providing specific physical partitioning, but it ispreferred to provide partitioning that does not hinder the movement ofthe hearth or the material charged thereon to the boundary between eachof the melting zone and the cooling zone or the reducing zone foreffectively maintaining a high temperature in the melting zone.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) and 1(b) are explanatory views of a traveling hearth furnace,used in the Japanese publication sho 63-108188, FIG. 1(a) being inperspective and FIG. 1(b) showing portions of the furnace in section.

FIGS. 2(a), 2(b), 2(c) and 2(d) are explanatory views in perspective inaccordance with this invention, showing sequential steps of stacking ofraw material on a hearth applicable to the present invention and changesof state upon reducing the raw material and melting the reduced product.

FIGS. 3(a) and 3(b) are, respectively, in section and in perspectiveexplanatory views of one form of lamination condition used in anexperiment hereinafter described in accordance with this invention.

FIG. 4 is an explanatory sectional view, with parts shown in section, ofapparatus for heating used in the experiment of FIGS. 3(a) and 3(b).

FIGS. 5(a) and 5(b) are explanatory views of lamination conditions inanother experiment in accordance with this invention.

FIGS. 6(a) and 6(b) are similar explanatory views showing laminationconditions in an alternative experiment in accordance with thisinvention.

FIG. 7 is an explanatory view, in perspective, showing a travelinghearth furnace used in one example according to this invention.

FIG. 8 is an explanatory view, in perspective, with a portion cut awayto show important details, showing a discharging device used in anexample according to this invention.

FIGS. 9(a) and 9(b) are explanatory sectional views showing laminationconditions of a raw material used in an example according to thisinvention, and referred to in Table 4 hereinafter as LaminationCondition A.

FIGS. 10(a) and 10(b) are explanatory sectional views of anotherlamination condition of raw material used in an example and referred toin Table 4 hereinafter as Lamination Condition B.

FIGS. 11(a) and 11(b) are explanatory sectional views of an alternativelamination condition of raw material adopted in another example, andreferred to in Table 4 hereinafter as Lamination Condition C.

FIGS. 12(a) and 12(b) are explanatory sectional views of anotheralternative lamination condition of raw material adopted in anotherexample, and referred to in Table 4 hereinafter as Lamination ConditionD.

FIGS. 13(a) and 13(b) are further explanatory views of a laminationcondition of raw material adopted in Example 3 herein.

FIG. 14 shows a preheating device for a raw material as adopted inExample 7 herein.

FIG. 15 is a detailed view of charging device used in one exampleaccording to this invention shown in FIG. 7.

In the drawings, the reference numerals are as follows: 1: Solidreducing material layer; 1 a: Concave portion of solid reducing materiallayer; 2: Raw material; 2 a: Powder mixture as a raw material; 3:Reduced product; 4: Metal; 5: Slag; 10, 10′: Furnace body; 10 a:Preheating zone; 10 b: Reducing zone; 10 c: Melting zone; 10 d: Coolingzone; 11, 11′: Hearth; 13, 13′: Burner; 14: Charging device; 14-1:Charging device of solid reducing material; 14-2: Charging device of rawmaterial; 14-3: Roller having convex portions; 15: Discharging device;16: Lifting device; 17: Cooler; 18: Crusher; 21: Raw material (lowerlayer); and 22: Raw material (upper layer).

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The “reducible material” referred to herein may be any metallic rawmaterial that is capable of being reduced. Typical examples include ironore, or Cr ores, Ni ores, iron sand, iron powder, blast furnace dust,steel-making dust, stainless refining dust, and iron-making sludgescontaining metal such as Fe, Ni and Cr, for example.

In the present invention, since the raw material containing thereducible material and the solid reducing material are charged on ahearth, the raw material is reduced by heating and then melted at leastonce, the metal in the reduced product can be easily separatedmechanically from the slag. Accordingly, when the reduced metal is usedas a starting material, for example, as feed into an electric furnace,since the slag is not present, less calcium oxide is needed to controlthe slag CaO/SiO₂ ratio for dephosphorization and desulfurization, inthe electric furnace operation.

Further, in the present invention, when particles of the solid reducingmaterial are supplied so as to be laid entirely on the hearth to form asolid reducing material layer, and the raw reducible material is stackedon the solid reducing material layer, a carbon source can be alwayssupplied from the solid reducing material layer on the hearth to themetal-containing material in the raw material, particularly, to themolten metal, even after the solid reducing material in the raw materialhas been thoroughly consumed by the reducing reaction, and the reducedproduct (metal) is not reoxidized.

This means that a reducing atmosphere is always present just above theraw material layer and the reduced product layer, even when an oxidizinggas might be stagnating in the upper portion of the furnace. With suchconstitution, the reduced metal can always be produced stably even iffurnace operations for the reduction and melting should become changed.Further, if the raw material includes a segregation step and the solidreducing material in the raw material is insufficient locally, thecarbon content can be supplemented by carbon from the solid reducingmaterial layer just beneath the stacked layer of the raw material, andthe reducing reaction can take place smoothly.

Furthermore, presence of the solid reducing material layer preventsdirect contact between the molten metal of the reduced product and thehearth. This prevents erosion of the hearth by the molten metal.

Furthermore, it is important in the present invention that the reducedproduct is physically dispersed in a multiplicity of so-called islandpatterns to make a multiplicity of discrete products, each of anappropriate size, on the hearth—created by the spotwise dispersion. Thatis, the materials are so arranged that the molten reduced product, evenafter re-solidification on the hearth, is dispersed as a multiplicity ofislands that are separate from each other, so that individualcoagulation products have small sizes and reduced weights, allowing themto be discharged easily from the furnace and collected.

Further, when large re-solidified products are discharged to the outsideof the furnace, they tend to exert an impact shock on the hearth.However, individual solidified “island portions” are smaller and reducedin weight, and give an impact shock that is sharply decreased, reducingthe danger of injuring the hearth.

Further, for discharging the solidification products of the formed metaland slag to the outside of the furnace, it is necessary that the furnacebody has a discharge port of a size at least larger than each solidifiedproduct, or an opening for locating a discharging device for dischargingthe products. The sizes of discharge ports can be decreased as the sizeof the products is smaller, to facilitate sealing between the inside andthe outside of the furnace.

It is effective, to assure the spotwise presence of a multiplicity ofreduced-size metallic products, to form a plurality of concave portionsin the upper surface of the solid reducing material layer. This isbecause the raw material charged into and stacked on the solid reducingmaterial layer is reduced by heating and further melted to form metaland slag, and the metal and the slag are solidified by cooling andsolidified separately, having been moved by surface tension into each ofthe concave portions on the surface of the solid reducing materiallayer.

In the raw material charged and stacked on the hearth or on the solidreducing material layer, the volatile substances contained in the rawmaterial are converted into waste gases during heating-reduction, andoxygen contained in metal oxide is also reduced by the solid reducingmaterial and converted into waste gases. Accordingly, what remains onthe hearth are the molten metal ingredient, the gangue ingredient suchas SiO₂ and Al₂O₃ and the solid reducing material.

A preferred embodiment of the present invention will now be explainedwith reference to the drawings.

Prior to charging of the raw material, granular solid reducing materialis scattered on the rotationally moving hearth to form a solid reducingmaterial layer. The solid reducing material layer formed on the hearthcan basically be an aggregate of reducing materials. Since this reducinglayer is not mixed with the metal-containing reducible material, itscarcely changes except for the loss of volatile matter duringoperation. Usually, the solid reducing material contains about 10% ashbut most of the balance comprises a carbonaceous material and maintainsa solid state even at a high temperature of about 1000 to 1500° C.Accordingly, the solid reducing material layer itself does not fuse tothe refractory on the upper surface of the traveling hearth. Itfunctions as a protective layer for the refractory on the hearth.

On the solid reducing material layer, a mixture of the metal-containingmaterial and additional solid reducing material is charged and stacked.Stacking may be accomplished in a variety of ways, as hereinafterdescribed, to create a multiplicity of islands of reducible metallic rawmaterial, individually dispersed separately from each other, in the bodyof the solid reducing material. An alternative is a mixture of themetal-containing material, the solid reducing material and auxiliary rawmaterial. Reduction is caused by heating during rotational movement ofthe hearth in the furnace. The reduced material is further heated untilit is melted, and the reduced product (metal and slag) formed isdispersed spotwise in an island pattern as heretofore described. Thismeans that reduced metal arranged into a predetermined product size canbe produced continuously.

FIG. 2(a), FIG. 2(b), FIG. 2(c) and FIG. 2(d) of the drawings are viewsof examples of raw material laminate structures on the hearth in atraveling hearth furnace. They assist in understanding the process ofreduction and melting.

Referring to FIG. 2(a), a solid reducing material 1 is. at first laid onthe surface of the moving hearth 11 to cover the surface with solidreducing material layer 1, and a plurality of concave cup-like portionsor pockets 1 a are preferably formed on the upper surface of the solidreducing material layer 1. Then, the raw material 2 is charged as inFIG. 2(b) and stacked in the pockets 1 a and on the thus formed solidreducing material layer 1. Subsequently, reduction takes place byheating using (for example) a burner 13 (FIG. 1(b)) at an upper portionof the furnace body. As a result, as shown in FIG. 2(c), themetal-containing material in the raw material 2 shrinks under the effectof the solid reducing material (incorporated carbonaceous material)mixed together, to form a reduced-size product 3 containing the gangueand, at the same time, to form a slag mainly comprising the ash of thesolid reducing material used as the reducing material contained in theraw reducible metallic material. Since the solid reducing material inthe raw reducible metallic material is consumed by the reductionreaction (although the extent may differ depending on the blendingmethod of the raw material and the metal-containing material and solidreducing material to be used), the volume of the reduced product and theash containing gangue (reduced product 3 of FIG. 2(c)) is decreased,compared with that of the original raw reducible material.

Auxiliary raw metallic material may preferably be added to the main rawmaterial for facilitating melting of the reduced product and the ash.Steel making slag, limestone, fluorspar, serpentine, dolomite and thelike are suitable examples. Although this introduction causesevaporation of combined water and decomposition reaction of a portion(for example, CaCO₃ as the main ingredient of limestone is thermallydecomposed into CaO) before melting, but they remain in a solid state.

Then, as the heating of the raw material proceeds further, the rawmaterial and the auxiliary raw material are not merely reduced but startmelting and, as shown in FIG. 2(d), are melted and separated into metal4 and slag 5. Since the raw material comprising the metal-containingmaterial and the solid reducing material, or the raw material comprisinga mixture of the metal-containing material, the solid reducing materialand the auxiliary raw material are dispersed spotwise in the cups ordepressions in the solid reducing material layer 1, the metal 4 and theslag 5 are formed in the cups in the solid reducing material layer 1. Inthis case, as shown in FIG. 2(d), when concave portions or cups 1 a areformed on the surface of the solid reducing material layer 1, the metal4 as the reducing product and the slag 5 are spontaneously moved to andcontained in various ones of the cup-shaped concave portions 1 a of thesolid reducing material layer 1 by surface tension and gravity, and arephysically divided into units corresponding to each concave portion 1 aon the solid reducing material layer 1. Lumps of the metal 4 and theslag 5 are present spotwise in a so-called island pattern.

As described above, when the reduced product is dispersed in concaveportions la formed in the solid reducing material layer, the metal andthe slag are formed in an appropriate size for further handling. Inaddition, since the volume of the thus formed metal and slag is onlyabout 10 to 60% of the volume of the raw material, they are arrangedspotwise, buried in the solid reducing material, so that they are not incontact with each other.

Since the specific gravity of the metal and the slag is higher than thatof the solid reducing material layer 1, it may be considered that theysubmerge under the solid reducing material layer 1. However, the metaland the slag actually form individual small lumps and, due to the effectof surface tension, they remain on or near the surface of the solidreducing material layer.

The slag and the metal thus formed on the rotational moving hearth reachthe cooling zone and are cooled. This separates solid lumps of slag 5from solid lumps of reduced metal 4. All this time the solidified metaland the solidified slag are kept apart from the hearth by the presenceof the underlying solid reducing material layer. They form individualsmall lumps, and can be discharged easily from the furnace.

If the surface of the solid reducing material layer 1 is made in a flatshape without forming concave portions, the metal and the slag aftercooling would not be divided and sometimes may form larger lumps. Insuch a case a crusher for crushing the metal and the slag on the hearthmay be necessary upon discharging from the furnace. Accordingly, it ispreferred that concave portions are formed, preferably on the surface ofthe solid reducing material layer 1.

This has been confirmed also by experiments conducted by the inventorsregarding the surface shape of the solid reducing material layer. Inthese experiments, powdery iron ores, powdery cokes and limestones eachof a grain size of 8 mm or less were mixed at a 7:3:1 by weight ratio toform a powder mixture as the raw material. Then, concave and convexportions were formed on the surface of the solid reducing material layer1 made of powdery cokes on the basis of the material laminationcondition shown in FIGS. 3(a) and 3(b), on which a powdery mixture 2 wasstacked, which was placed in an experimental apparatus as shown in FIG.4, kept at a temperature of 1480 to 1500° C., and reduced and melted toform metal and slag. The results of the experiment are shown in Table 1.FIG. 4 shows an example of the apparatus used for the experiment. It hada structure in which a hearth 11′ was vertically moved by a liftingdevice 16 and placed in a furnace body 10′. The solid reducing materiallayer 1 and the material deposition layer 2 a formed on the hearth 11′were heated by a burner 13′, exposed to the same thermal hysteresis asdescribed above, and reduced and melted.

Regarding the shape of the concave portions formed in the solid reducingmaterial layer 1, experiment was conducted also on a square shapemolding 2″ as shown as an alternative in FIGS. 5(a) and 5(b). The samewas done on a combination of circular shapes of depressions 1(a) ofdifferent sizes, as shown in FIGS. 6(a) and 6(b). In Table 1, theexpression “hole shape” means the shape and size of the concave portionor cup-shaped depression formed in the solid reducing material layer 1.“L” in Table 1 shows the diameter of a circle having an area identicalwith that of the hole of the shape (equivalent circle diameter). In acase of forming various different shapes as in the raw materiallamination condition of FIGS. 6(a) and 6(b), the maximum value amongthem is shown.

Each of FIGS. 3(a) , 5(a) and 6(a) shows the cross-sectional shape of aconcave portion la formed on the surface of the solid reducing materiallayer 1, which includes the greatest layer thickness L₁ of the materialpowder and the smallest layer thickness L₂ of the raw material at theconvex portion on the surface of the solid reducing material singlelayer. As shown in Table 1, after the experiment, separate lumps ofmetal were obtained in a dispersed form in each of the resulting concaveportions.

TABLE 1 Raw material L1/ Shape of metal Temp. lamination Hole shape L L2after experiment (° C.) condition (mm) (mm) (-) (mm) 1 1500 1 Round 5050 1.1 Round 46-52 2 1500 1 Round 50 50 1.2 Round 44-52 3 1500 1 Round50 50 1.5 Round 45-53 4 1480 1 Round 50 50 1.1 Round 43-51 5 1480 1Round 50 50 1.2 Round 48-54 6 1500 1 Round 80 80 1.4 Round 61-83 7 15001 Round 100 100 1.4 Round 83-92 8 1500 1 Round 300 300 l.4 Round 248-2919 1500 1 Round 300 300 1.2 Round 231-285 10 1500 2 Square 109 1.4Rod-shape, 185 × 50 length 161-176, width 43-51 11 1500 2 Square 214 1.4Rod-shape, 360 × 100 length 342-361, width 88-97 12 1500 3 Round 200 1.4Round 183-190, 200 & 50 36-42 NOTE: Lamination conditions 1 appears inFIGS. 3(a) and 3(b). Lamination conditions 2 appears in FIGS. 5(a) and5(b). Lamination conditions 3 appears in FIGS. 6(a) and 6(b).

Each method formed a plurality of concave portions on the surface of thesolid reducing material layer comprising solid reducing materialparticle laid uniformly to a predetermined thickness. This is afundamental mode for forming the solid reducing material layer on thehearth. This forming method can reliably form a multiplicity of concaveportions, select easily from a variety of applicable shapes, and iseffective if periodicity is required for the concave portions. A rolleror a plate with a plurality of convex portions on its lower surface issuitably usable. Transfer of the surface pattern of the roller or theplate to the surface of a solid reducing material layer makes itpossible to form a plurality of concave portions on the surface of asolid reducing material layer.

Another alternative method of stacking in accordance with this inventioncomprises laying particles of a solid reducing material on a hearth to aconstant layer thickness, dropping raw material lumps of briquette-likeshape from above, thereby forming concave portions as a product of theresulting impact shock and, further, charging other metal-containingmaterial and solid reducing material between the stacked briquettes toform a stacked layer having a predetermined layer thickness, and havingconcave portions spaced apart from each other as heretofore described.

A method comprising dropping a mixture of raw material lumps and anotherfine raw material onto the surface of the solid reducing material layercan be used.

A still further stacking method involves preliminarily laying a solidreducing material entirely as an underlayer, and charging and stacking araw material, onto the surface thus obtained, a solid reducing materiallayer of a predetermined layer thickness, stacked so as to form aplurality of uneven protuberances on the surface of the raw materialstacked layer. That forms unevenness by controlling a stacked layer ofthe charged raw material instead of forming the concave portions 1 a ofthe solid reducing material layer 1 on the hearth floor. It can performsubstantially the same function and achieve substantially the sameeffect as the embodiments previously mentioned. After melting, metal andslag generated around the convex portions of the raw material stackedlayer are gathered to the metals the slags generated at the convexportions by surface tension. Accordingly, the metals the slags are keptpresent spotwise and held on the surface of the solid reducing materiallayer. Therefore, the same function and effect can be substantiallyattained. Charging and stacking raw material lumps onto the surface ofthe solid reducing material layer dispersed as island patterns attainsubstantially the same function and effect.

The solid reducing material layer laid on the hearth serves as acarburizing source for the molten metal, and supplies carbon to themolten metal, compensates reducing reactions of the raw material, andprevents direct contact between the molten matter and the hearth.Further, it prevents erosion of the hearth by the molten matter.

Accordingly, so long as substantially these functions are ensured, thesolid reducing material layer may contain other materials than thecarbonaceous material. For example, the solid reducing material layermay be mixed uniformly with a flux or as a gradient blending ofnon-uniform concentration, or the flux may be applied only on thesurface of the solid reducing material layer. The mixed flux serveseffectively for reducing the quantity of S in the molten metal byabsorption of the S ingredient in the solid reducing layer.

As the constituent ingredients of the solid reducing material layer,coal chars, cokes, non-coking coals, coking coals and anthracites can beused. They contain carbon material, serve as a carburizing source forthe molten metal, supply carbonaceous material to the molten metal andcompensate the reduction.

Among the solid reducing materials, there are those softened and meltedby heating, such as coking coal. They may sometimes shrink subsequentlyand develop macrocracks, which may result in the possibility that themolten matter on the solid reducing material layer will penetrate to thecracks. However, direct contact between the molten matter and the hearthcan be prevented by laying the solid reducing material layer on thehearth, specially in case the solid reduced layer is not softening andnot melting at least in a portion contacting with the hearth so as toprevent erosion of the hearth by the molten matter reliably.

Since the softening and melting behavior of the solid reducing materialchanges, depending on the kind of solid reducing material and the kindof heating pattern, the layer thickness and the kind of carbonaceousmaterial to be laminated are properly selected depending on theoperating conditions and the solid reducing material to be used.

The solid reducing material layer has the function and effect asdescribed above. If the amount of the layer laid on the hearth is toosmall, it cannot sometimes function since it may be consumed bycarburization and reduction. Even if it is not consumed, the effect ofthe layer of solid reducing material on the hearth may possibly bepartially lost due to vibrations of the furnace. Therefore, thethickness of the solid reducing material layer laid on the hearth isdesirably about 5 mm or more and, more preferably, about 10 mm or morein order to prevent direct contact between the molten matter and thehearth, and to ensure the prevention of erosion of the hearth by themolten matter.

When the raw material containing the metal-containing material and thesolid reducing material is charged and stacked on the solid reducingmaterial layer, not only the raw material of a single species need bestacked to a predetermined layer thickness but also different kinds ofraw materials may be laminated in a multi-stage arrangement. Forinstance, a reducing metal can be obtained with no trouble by laminatinga raw material, comprising a fairly reduced metal-containing materialand a solid reducing material at a blending ratio enough to reducemetal-containing material, on the surface of the solid reducing materiallayer and laminating a raw material comprising a metal-containingmaterial and a different solid reducing material. In the case of thefairly reduced metal-containing material, reduction proceeds morerapidly than usual, the melting and carburization occur sooner, andreduction and melting in the upper layer are promoted since meltingstarts therefrom to assist the effect of the present invention.

Further, in charging the raw material, the raw material is segregatedintentionally by particle percolation in which large particles arestacked below and smaller particles are distributed thereon in the rawmaterial stacked layer. This charging method is also application exampleof the present invention.

In the case of multi-stage laminating of different kinds of rawmaterials, the metal-containing material and the solid reducing materialare distributed at different blending ratios. Also, the particularspecies of metal-containing material and solid reducing material may bevaried, using variants such as lamination of blast furnace dry collecteddusts at an upper layer, and raw materials containing iron ores andsolid reducing material at a lower layer.

The metal and the slag, after cooling, may be crushed on the furnacehearth such that they are easily discharged using a crusher in whichlumps of metal and slag are formed. Further, even small lumps of metaland slag, obtained by spotwise holding and cooling the molten particleson the surface of the solid reducing material, may be in part broken topieces by mechanical processing outside of the furnace. Further, thesolid reducing material laid on the hearth may be discharged from thefurnace, depending on the recovery method used.

As has been described above, it is most convenient to recover theagglomerates of the metal and the slag by sieving products outside ofthe furnace. A mixture of powdery metal, powdery slag and powdery solidreducing material can also be obtained after passing through the sieve.

The mixture of the powdery metal or powdery slag and the remainingpowdery solid reducing material, after passing through the sieve, may berecovered and added to the raw material to be charged and then suppliedagain to the furnace, thereby attaining complete recycling of metal,slag and solid reducing material.

Improvement of the recovery ratio of the metal and decrease of theamount of solid reducing material can be attained. When the recoveredpowders passing through the sieve are charged on the solid reducingmaterial layer, the technique of multistage lamination with differentkinds of raw materials may be used.

As another preferred embodiment of the present invention, it isparticularly effective to incorporate highly volatile metallic elementssuch as raw Zn and Pb into the raw material to be charged. This isbecause Zn and Pb in the raw material are easily vaporized by heatingand pass into the waste gases. Then, Zn and Pb ingredients can berecovered effectively by quenching the waste gases, such as with a waterblow. When iron, Cr, Ni or the like is also contained in the rawmaterial and will remain on the hearth, the Zn, Pb ingredients and theFe, Cr, Ni ingredients can be separated spontaneously. Accordingly, whenusing such raw material, preparation of Zn and Pb of high quality, andpreparation of high quality Fe, Cr, or Ni can be achieved.

Zn and Pb may be sometimes reoxidized into a solid state, depending onthe temperature of the waste gases and the oxygen partial pressure, butthey have extremely small grain sizes and are entrained in the wastegases and discharged from the furnace.

In the furnace operation by the method according to the presentinvention, when the raw material charged and stacked on the hearth ismelted, and if the atmosphere in the furnace is of a reducing nature,the oxygen partial pressure is lowered and carburization of the solidreducing material laid on the hearth to the metal can be conductedrapidly. Furthermore, if the atmosphere is controlled by a carboncontaining gas, carburization from an atmospheric gas can also beconducted. This can lower the melting point of the metal to therebypromote melting and increase productivity. Furthermore, the oxygenpartial pressure can be lowered to effect the sulfur distributionbetween the slag and the metal to effectively reduce the percentage ofsulfur in the metal.

It is important to form a reducing atmosphere in the furnace. The sameeffect can be obtained by supplying a reducing gas to cover the rawmaterial layer stacked on the hearth and, particularly, by forming areducing atmosphere at least for the melting zone. When heating byburner combustion, the atmosphere in the entire furnace may be renderedreducing by adjusting the combustion control of the burner. Also, areducing gas may be introduced in the vicinity of the material layersurface, using a separate route.

Further, it is effective to preheat the raw material prior to chargingit into the furnace. If mixed raw materials are preheated outside of thefurnace, the coal may be softened enough to melt, which causes handlingproblems in the preheating step, depending on the kind of coal used andthe preheating temperature.

In such a case, preheating for improvement of productivity may be usedentirely or partially except for the solid reducing material in the rawmaterial mainly comprising the metal-containing material and the solidreducing materials at the outside of the traveling hearth furnace,mixing the raw material just before supplying it to the traveling hearthfurnace, agglomerating optionally and supplying to the traveling hearthfurnace, thereby improving the productivity while avoiding handlingproblems.

In another preferred embodiment of the present invention, the residencetime of the raw material in the furnace, from the feed to the dischargeof the raw material, may be as long as about an hour, more or less,although it varies depending on the manner of charging the raw materialand the furnace temperature. If the heating of the raw material can bespeeded up, productivity of the furnace can be improved. By preheatingthe raw material, the residence time in the furnace can be shortened.

For heating the traveling hearth furnace, burner combustion can beconveniently employed. The burner may be supplied with fuels such asnatural gas, coke furnace gas, heavy oil, or the like, along withcombustion gases such as air and oxygen, for example. Preheating of thefuel or the combustion gases by heat exchange with waste gases from thefurnace can conserve on fuel to the burner.

When burner combustion is adopted, since the temperature of the wastegases released from the traveling hearth furnace is about 1000° C. orhigher, it is preferred to utilize waste gases for preheating the rawmaterial outside of the furnace. This can improve productivity of thefurnace as described above, and can eliminate the requirement ofsupplying energy for preheating the raw material.

The raw material charged in the furnace is melted after reduction. Forthis operation, it is necessary to provide high-temperature refractoryand furnace body structure. This results in increased installation cost.While the reduction of the raw material proceeds faster when thetemperature is higher, a practical reducing rate can be ensured even ifthe temperature is not so high as to cause melting. On the other hand,if the melting zone is unnecessarily short, this slows the moving speedof the hearth in order to ensure the reaction time necessary formelting, thereby lowering productivity. The length of the zone formelting is selected appropriately to considerations of maintenance,productivity and minimization of installation cost.

Products such as metal and slag melted on the hearth are gathered andsolidified before discharging from the furnace. Then fuels such asnatural gas, coke furnace gas and heavy oils and combustion aids such asair or oxygen supplied to the burner are also able to have a role ascooling medium

In this case fuels and combustion aids are preheated and this preheatingachieves decrease in production energy. Further, products such as themetal and the slag may be cooled by using, for example, nitrogen orreducing gas, which can also be used for controlling the atmosphere ofthe furnace during melting.

When the metal and the slag are discharged from the furnace, not onlythe metal and the slag but also the solid reducing material layer may bedischarged partially or entirely depending on the discharging apparatusand method. Alternatively, substantially only the metal and the slag canbe discharged, with the bed of solid reducing material left in place onthe hearth. When the furnace is a rotary furnace and the solid reducingmaterial is discharged only partially or in a small amount, the solidreducing material is kept without change on the hearth. In this case,the solid reducing material is supplied at the raw material supplysection in an amount proportional to any material consumed.

EXAMPLES Example 1

In this example, the operation described below was conducted using arotary hearth furnace as shown in FIG. 7. The rotary hearth of 2.2 meterdiameter was provided with an alumina refractory on the upper surface(as in FIG. 1(b)) and they were housed in an annular furnace body as inFIG. 1(b), in which a burner is disposed above the hearth.

As shown in FIG. 7, the hearth of the rotary furnace was divided into apreheating zone 10 a, a reducing zone 10 b, a melting zone 10 c and acooling zone 10 d. A raw material layer 2 was formed on the rotaryfurnace hearth by charging and stacking a raw material mainly comprisingan iron-containing material and a solid reducing material. In thisfacility, reference numerals identical with those shown in FIGS. 1(a)and 1(b) denote similar parts. The number 17 in FIG. 7 denotes a coolerdisposed in front of a discharge port for cooling reduced iron and slag.

FIG. 8 is a schematic view taken near the furnace exit port used for theoperation. After discharging solid metal by discharge device 15, themetal and the slag were separated by magnets. A crusher 18 was usedoptionally, depending on the case.

The raw material at the supply port of the furnace was charged andstacked using metal-containing material and a solid reducing material,using the charging device 14. This was done under four sets ofconditions shown as lamination examples of the raw material asillustrated in FIGS. 9(a) and (b), FIGS. 10(a) and (b), FIGS. 11(a) and(b) and FIGS. 12(a) and (b). In this case, concave portions were formedon the surface of the solid reducing material layer by pressing a rollerhaving convex portions down on the surface of the solid reducingmaterial layer.

As the metal-containing material, iron ore having compositions as shownin Table 2, containing 7% or more of gangue ingredient (SiO₂, Al₃O₃,etc.) were used. The solid reducing materials had ingredientcompositions shown in Table 3 containing 6 to 11% of ash ingredient.They were used while controlling their mesh sizes to 3 mm or less.

The results are shown in Table 4. Nos. 1 to 6 showing applicationexamples are examples of the present invention. In any of conditions forthe examples of the stacked form shown in FIGS. 9(a) and 9(b), therefractory material for the hearth was undamaged. There was nodifficulty discharging products. The iron recovery rate for the productswas as high as 97.4% or more. The products could be recoveredsubstantially free of gangue and ash ingredients. There was nosignificant reduction of productivity. In No. 5, a portion in whichmetal and slag in 2 to 3 concave portions were joined into a largermass, but there was no particular problem regarding smooth andsuccessful discharge.

Application Examples Nos. 7 and 8 are examples of stacked shapes ofFIGS. 10(a) and 10(b), in which the raw material was partitioned intosmall areas by the solid reducing material and arranged in a spotwisemanner on the solid reducing material layer, so as not to come intodirect contact with the hearth. Under the lamination condition, sincethe reduced iron and the ash were separated by the solid reducingmaterial layer from the hearth refractory, even when they were meltedfor the purpose of removing gangue and ash ingredient, the hearthrefractory was not damaged by the slag and the molten iron. However,since the solid reducing material layer was already exposed to thesurface upon stacking, utilization of the radiant heat to this portion,though acceptable, was somewhat lacking, and productivity was somewhatlower as compared with Examples Nos. 1 to 6.

Application Examples Nos. 9 and 10 are examples under laminationconditions shown in FIGS. 11(a) and 11(b), in which a solid reducingmaterial layer 1 had a smooth upper surface and a powdery reduciblematerial mixture was stacked in a layered shape over the layer 1. Inthese examples, when the reduced iron and the ash were melted forremoving gangue or ash ingredients, both the slag and the metal formedinto large plate-like shapes and, although being partially cracked dueto shrinkage in the cooling process, the metal and the slag aftercooling formed large plate shapes, some of which extended from thedischarge port to the vicinity of the cooler 17 of FIG. 8.

A crusher was disposed before the discharging device for crushing theproducts on the hearth before discharging out of the furnace. Althoughthe installation cost and the running cost were increased by theinstallation of the crusher, the operation was assisted by the crusherand metal was produced.

Application Example No. 11 involved lamination as in FIGS. 12(a) and12(b), in which raw material 2 was placed in a layered shape on thehearth refractory 11 without any intervening solid reducing materiallayer. The reduced iron and the ash were melted for removing gangue andash ingredients. Since the raw material was carried directly on thehearth refractory surface, the hearth refractory suffered from meltingloss by molten materials. Further, some of the slag and the metal hadlarge plate-like shapes that extended from the discharge port in thevicinity of the cooler 17 in FIG. 8. A crusher was disposed at a side ofthe discharge device and the products were crushed on the hearth beforedischarging to the outside of the furnace. Although the installationcost was increased by the installation of the crusher, and the runningcost of electric power necessary for the operation of the crusher, andthe cost regarding some melting loss of the hearth refractory materialincreased, the operation was possible and the metal could be produced.

In each of Examples Nos. 1 to 10, the solid reducing material layer 1 atportions in contact with the hearth was not softened and melted near thedischarge portion.

TABLE 2 Combined water T.Fe FeO SiO₂ Al₂O₃ CaO MgO P S (%) (%) (%) (%)(%) (%) (%) (%) (%) 3.25 62.30 0.11 4.31 2.60 0.04 0.05 0.075 0.014

TABLE 3 Volatile matter (%) Ash (%) I Non-coking coal 44.5 6.6 II Coalchar 3.0 10.4

TABLE 4 Solid reducing material Sub raw Product Pro- I II Ore materialGangue + Lami- Iron Gangue ductivity (mass (mass (mass (limestone) ashnation Damage recovery ingredient (5) %) %) %) (mass %) (mass %) con- Lof hearth rate (mass %) kg-DRI/ (1) (1) (1) (1) (2) dition (mm) L₁/L₂refractory Crusher (%)(3) (4) hour Remarks 1 26.7 66.3 7.0 10.3 A 50 1.2none none 98.2 0.1 128 Application Example 2 26.7 66.3 7.0 10.3 A 300 1.4 none none 97.9 0.1 130 Application Example 3 17.6 75.4 7.0 11.0 A300  1.2 none none 98.6 0.2 126 Application Example 4 17.6 75.4 7.0 11.0A 50 1.4 none none 98.4 0.1 129 Application Example 5 26.7 66.3 7.0 10.3A 50 1.1 none none 97.8 0.2 122 Application Example 6 13.4  8.8 70.8 7.011.0 A 200  1.4 none none 97.6 0.2 123 Application Example 7 26.7 66.37.0 10.3 B 50 —(6) none none 97.5 0.2 105 Application Example 8 17.675.4 7.0 11.0 B 50 —(6) none none 97.6 0.2 103 Application Example 926.7 66.3 7.0 10.3 C — — none used 97.8 0.2 124 Application Example 10 17.6 75.4 7.0 11.0 C — — none used 97.7 0.2 122 Application Example 11 26.7 66.3 7.0 10.3 D — — damaged used 95.3 1.5 119 Application Example(1)Blending ratio in raw material (2)Ratio of gangue + ash in rawmaterial (3)Fe content in product relative to total content in rawmaterial (4)Ratio of other matters than metal intruded in product(5)Amount of product per 1 hr (6)Numerical value corresponding to L₂ cannot be defined for lamination condition (B) NOTE: Lamination condition Aappears in FIGS. 9(a) and 9(b). Lamination condition B appears in FIGS.10(a) and 10(b). Lamination condition C appears in FIGS. 11(a) and11(b). Lamination condition D appears in FIGS. 12(a) and 12(b).

Example 2

The following operation was conducted using the apparatus of Example 1.The raw material was charged and stacked at the supply port of thefurnace by the charging device 14 on the rotary hearth 11 under thelamination condition shown in FIGS. 9(a) and 9(b) (Lamination ConditionA). Limestone was added in an amount of 5% by weight into the solidreducing material layer 1. As shown in Table 5, it was found that thepercentage of sulfur (S) was lowered in the recovered metal, in caseswhere limestone was blended with the solid reducing material layer,under substantially the same operation conditions.

TABLE 5 Limestone in Solid reducing Sub raw material Gangue + solidreducing material Ore (limestone) ash material layer [% S] Productivity(mass %) (mass %) (mass %) (mass %) (mass %) Lamination L (mass %)kg-DRI/hour (1) (1) (1) (2) (3) condition (mm) L₁/L₂ (4) (5) Remarks 1217.6 75.4 7.0 11.0 0 A 50 1.2 0.72 126 Application Example 13 17.6 75.47.0 11.0 5.0 A 50 1.2 0.49 125 Application Example 14 17.6 75.4 7.0 11.05.0 A 50 1.4 0.53 129 Application Example (1)Blending ratio in rawmaterial (2)Ratio of gangue + ash in raw material (3)Ratio of limestonecontained in solid reducing material layer (4)Ratio of sulfur containedin metal product (5)Amount of product per 1 hr

Example 3

Using the apparatus of Example 1, the following operation was conducted.The raw material was stacked at the supply port of the furnace by thecharging device 14 under the lamination condition or in the multi-layerform for the raw material in FIGS. 13(a) and 13(b). In these figures,the raw material (lower layer) 21, and the raw material (upper layer) 22were different in the blend, as shown in Table 6. In Application Example16, not only the iron-containing material in Table 2 but also powderypig iron in Table 7 were blended as metal-containing materials to theraw material (lower layer) 21. As shown in Table 6, good production wasachieved even at a high rotational speed, under the condition ofblending the powdery pig iron to the raw material (lower layer) 21,where the amount of iron charged per unit area was identical and theoperation conditions other than the rotational speed of the furnace weresubstantially identical. The production speed was accordingly increased.In the Application Example 17, blast furnace dry collection dust inTable 9 was used for the raw material upper layer 22 and the identicalmaterial as that in Application Example 16 was used for the raw materiallower layer 21.

Since the properties of the raw material in the upper layer weredifferent, the productivity could not be compared directly, butproduction was conducted with no trouble.

TABLE 6 Sub raw Solid material Blast furnace Iron reducing (lime- drycollected Gangue + charged Rotational material Ore stone) Pig iron dustash amount Lami- speed (mass %) (mass %) (mass %) (mass %) (mass %)(mass %) (kg/m²) nation L RPM (1) (1) (1) (1) (1) (2) (3) condition (mm)L₁/L₂ (4) Remarks 15 17.6 75.4 7.0 0.0 0.0 11.0 23.1 A 50 1.2 0.050Application Example 16 Upper 17.6 75.4 7.0 0.0 0.0 11.0 10.9 A 50 1.20.058 Application layer Example Lower 15.8 67.9 6.3 10.0 0.0 9.9 12.2layer 17 Upper 0.0 0.0 0.0 0.0 100.0 12.9 10.5 A 50 1.2 0.055Application layer Example Lower 15.8 67.9 6.3 10.0 0.0 9.9 12.6 layer(1)Blending ratio in raw material (2)Ratio of gangue + ash in rawmaterial (3)Charging amount of iron contained in each of raw materiallayers per unit hearth area (4)Number of rotations of hearth per minute

TABLE 7 C Si Mn P S (%) (%) (%) (%) (%) 3.2 0.33 0.32 0.13 0.021

Example 4

The following operation was conducted using the apparatus of Example 1.The raw material was charged and stacked at the supply port of thefurnace by the charging device 14 on the rotary hearth 11 under thelamination condition shown in FIGS. 9(a) and 9(b) (Lamination Condition.A). After discharging products formed on the solid reducing materiallayer by the discharging device 15, they were entirely sieved on a 3 mmsieve. The entire fractions passing the sieve were mixed to the rawmaterial and recycled. The amount recycled to the raw material was 1.5to 2% of the raw material. As shown in Table 8, the metal recovery ratewas increased when the operation conditions were substantiallyidentical.

TABLE 8 Solid Sub raw Recycled Iron Iron reducing material raw recoverycharged Rotational material Ore (limestone) material ratio amount speed(mass %) (mass %) (mass %) (mass %) (mass %) (kg/m²) RPM (1) (1) (1) (2)(3) (4) (5) Remarks 18 17.6 75.4 7.0 0.0 98.6 23.1 0.050 ApplicationExample 19 17.6 75.4 7.0 1.57 99.8 23.5 0.054 Application Example 2017.6 75.4 7.0 2.05 99.7 23.6 0.053 Application Example (1)Blending ratioin raw material excluding recycled raw material (2)Ratio of recycled rawmaterial returned to the raw material based on the entire raw material(3)Fe content in product based on entire Fe in the raw materialexcluding recycled raw material (4)Charged amount of iron contained inraw material layer per unit hearth area (5)Number of rotations of hearthper minute

Example 5

The following operation was conducted using the apparatus of Example 1.In this example, water was sprayed into the waste gases from the furnaceto cool the waste gases and trap and recover dust in the waste gases.The raw material was stacked by the charging device 14 on the hearth 11under the lamination condition shown in FIGS. 9(a) and 9(b) (LaminationCondition A). The raw material used in this example was dry collecteddust from a blast furnace containing Zn and Pb in addition to Fe as themetallic ingredients. Further, the dry collected dust contained aportion of the coke charged to the blast furnace. The composition isshown in Table 9. As a result, ZnO and metallic Pb were recovered insecondary dust trapped in the water. The Fe ingredient was scarcelypresent in the secondary dust. Further, most of metals melted,coagulated and recovered in the furnace were Fe, Zn and Pb were notpresent at all.

TABLE 9 t.Fe FeO SiO₂ CaO Al₂O₃ MgO Zn Pb S C Dry collected dust 43.51.72 6.00 3.20 3.15 0.54 1.13 0.52 0.74 19.7 from blast furnace

TABLE 10 Dry collected Fe (%) in dust from blast Iron charged RotationalPb (%) in Zn (%) in secondary furnace amount speed metal metal dust(mass %) (kg/m²) RPM (mass %) (mass %) (mass %) (1) (2) (3) (4) (4) (5)Remark 21 100.0 21.4 0.050 <0.01 <0.01 <0.01 Application Example(1)Blending ratio in raw material (2)Charged amount of iron contained inraw material layer per unit hearth area (3)Number of rotations of hearthper minute (4)Ratio contained in product metal (5)Ratio contained inrecovered secondary dust

Example 6

The following operation was conducted using the apparatus of Example 1.In this example, the temperature in the melting zone was compensated bycombustion of a pure oxygen-propane burner and the degree of oxidationof the waste gases after combustion was adjusted by controlling the airratio. The raw material was stacked by the charging device 14 on therotary hearth 11 under the lamination conditions shown in FIGS. 9(a) and9(b) (Lamination Condition A). The results of the operation are shown inTable 11. The productivity was increased somewhat by increasing thereducing property of the atmosphere where the degree of oxidation of thegas after combustion, namely, the reducing property of the atmosphere,and the operation conditions other than the rotational speed of thefurnace, were substantially identical.

TABLE 11 Solid Sub raw reducing material Gangue + Productivity Meltingmaterial Ore (limestone) ash kg-DRI/ zone gas (mass %) (mass %) (mass %)(mass %) Lamination L hour CO CO₂ (1) (1) (1) (2) condition (mm) L₁/L₂(3) (%) (%) Remarks 22 17.6 75.4 7.0 11.0 A 50 1.2 126 1.2 42.0Application Example 23 17.6 75.6 7.0 11.0 A 50 1.4 140 37.0 8.0Application Example (1)Blending ratio in raw material (2)Ratio ofgangue + ash in raw material (3)Amount of product per 1 hr

Example 7

The following operation was conducted using the apparatus of Example 1.In this example, a rotary kiln type preheating device with a one-meterinner diameter and a three-meter length was used as shown in FIG. 14, inwhich waste gases from the traveling hearth furnace was introduced.together with ores and the ores were preheated by the waste gases. Thetemperature of the waste gases was changed from 1000° C. to 1100° C.,and the preheated ores were heated to about 500° C. The preheated oreswere introduced into a mixer (1 m inner diameter, 3 m length), mixedwith a solid reducing material (coal in Table 12) at a normaltemperature and then stacked by the charging device 14 shown in FIG. 7on the hearth 11 of the traveling hearth furnace under the laminationconditions shown in FIGS. 9(a) and 9(b). The results of the operationare shown in Table 13. In an operation not preheating the ores, theenergy charged to the burner fuels and consumed solid reducing materialwas 7.0 Gcal/t-metal, whereas the required energy was reduced to about6.8 Gcal/t-metal when using the thus preheated ores.

TABLE 12 Volatile matter (%) Ash (%) 32.1 9.6

TABLE 13 Solid Solid reducing reducing Sub raw material materialmaterial Gangue + Productivity Table 3 II Table 12 Ore (limestone) ashkg-DRI/ Charged Preheating (mass %) (mass %) (mass %) (mass %) (mass %)Lamination L hour energy operation (1) (1) (1) (1) (2) condition (mm)L₁/L₂ (3) Gcal/t-metal Remarks 24 No 17.6 75.4 7.0 11.0 A 50 1.2 126 7.0Application Example 25 Yes 22.7 70.4 7.0 11.0 A 50 1.4 141 6.8Application Example (1)Blending ratio in raw material (2)Ratio ofgangue + ash in raw material (3)Amount of product per 1 hr

As has been described above according to the present invention, reducediron with no substantial impurities of gangue and ash, namely, reducediron highly evaluated as a raw material to be further refined in anelectric furnace or the like, was obtained inexpensively and reliablyfrom a metal-containing material and a solid reducing material by theuse of a traveling hearth furnace. Further, damage to the hearth cansurprisingly be avoided by forming a solid reducing material layer onthe hearth itself. Furthermore, handling of the reduced metal isradically improved by forming the reduced metal in a spotwise manner onthe solid reducing material layer on the hearth, thereby enabling theindustry to create a reduced metal in controllable product sizes that isvery suitable as a raw material for further processing in electricfurnaces.

What is claimed is:
 1. A traveling hearth furnace comprising ahorizontally moving hearth, a hearth body disposed above and coveringsaid hearth, a charging device positioned for charging on said hearthcombined materials comprising a reducible metal-containing material anda solid reducing material on the hearth, a heating means for heatingsaid combined materials on the hearth to reduce said metal-containingmaterial and make a reduced metal and a slag, and being capable ofreducing said metal when heated, to produce said metal plus slag, saidcharging device and heating means being positioned and operative to forma pattern of spaced depressions in said upper surface of ansolid-reducing material, a cooling means for cooling said reducedproduct and said slag, and a discharging means positioned and operativefor discharging said cooled reduced product and said slag, wherein, apreheating zone provided in said furnace for preheating said combinedmaterials to be charged, a reducing zone provided in said furnace forreducing said metal-containing material charged, a melting zone providedin said furnace for melting and reducing said metal-containing material,and a cooling zone provided in said furnace for cooling said moltenreduced product and said slag, and wherein said cooling zone is disposedin said furnace between said charging device and said dischargingdevice.
 2. A traveling hearth furnace comprising a horizontally movinghearth, a hearth furnace disposed above and covering said hearth, acharging device positioned and operative for charging combined materialscomprising a metal-containing material and a solid carbonaceous reducingmaterial on said hearth, said charging device being positioned andoperative to form a pattern of pocket depressions in an upper surface ofsaid solid-reducing material, a heater in said furnace positioned forheating said combined materials on said hearth to reduce saidmetal-containing material and make a reduced product and a slag in saidpocket depressions, and to provide a reducing atmosphere just above saidmetal-containing material, a cooler positioned for cooling said reducedproduct and said slag, and a discharger positioned and operative fordischarging said cooled reduced product and said slag, wherein, thereare further a preheating zone provided in said furnace for preheatingsaid combined materials to be charged, a reducing zone provided in saidfurnace for reducing said metal-containing material charged, a meltingzone provided in said furnace for melting and reducing saidmetal-containing material, and a cooling zone provided in said furnacefor cooling said molten reduced product and said slag, and wherein saidcooling zone is disposed in said furnace between said charging deviceand said discharging device.
 3. A moving hearth furnace as defined ineither of claims 1 or 2, wherein said furnace further comprises acharging device positioned and operative to charge a solid-reducingmaterial in a manner to provide a solid-reducing material layer whichsubstantially completely covers said hearth, said layer having an uppersurface having a multiplicity of spaced-apart depressions, and to chargesaid combined materials on said solid-reducing material layer.
 4. Theapparatus defined in claim 2, wherein said charging device is positionedand operative to deposit upon said hearth a layer of a solid-reducingmaterial which substantially covers said hearth, and to deposit uponsaid layer an upper deposit of said metal-containing material, therebypreventing direct contact between said hearth and the molten metalgenerated by said heating of said metal-containing material.
 5. Atraveling hearth furnace comprising a horizontally moving hearth, ahearth disposed above and covering said hearth, a charging devicepositioned for charging combined materials comprising a metal-containingmaterial and a solid carbonaceous reducing material on said hearth,heating said combined materials on said hearth to reduce saidmetal-containing material and make a reduced product and a slag, and toprovide a reducing atmosphere just above said metal-containing material,a cooler cooling said reduced product and said slag, and a dischargerpositioned and operative discharging said cooled reduced product andsaid slag, wherein, a preheating zone provided in said furnace forpreheating said combined materials to be charged, a reducing zoneprovided in said furnace for reducing said metal-containing materialcharged, a melting zone provided in said furnace for melting andreducing said metal-containing material, and a cooling zone provided insaid furnace for cooling said molten reduced product and said slag, andwherein said cooling zone is disposed in said furnace between saidcharging device and said discharging device, wherein said chargingdevice is positioned and operative to deposit upon said hearth a layerof a solid-reducing material which substantially covers said hearth, andto deposit upon said layer an upper deposit of said metal-containingmaterial, thereby preventing direct contact between said hearth and themolten metal generated by said heating of said metal-containingmaterial, wherein said charging device is positioned and operative toform a pattern of pocket depressions in said upper surface of saidsolid-reducing material layer.
 6. A traveling hearth furnace comprisinga horizontally moving hearth, a hearth disposed above and covering saidhearth, a charging device positioned for charging combined materialscomprising a metal-containing material and a solid carbonaceous reducingmaterial on said hearth, heating said combined materials on said hearthto reduce said metal-containing material and make a reduced product anda slag, and to provide a reducing atmosphere just above saidmetal-containing material, a cooler cooling said reduced product andsaid slag, and a discharger positioned and operative discharging saidcooled reduced product and said slag, wherein, a preheating zoneprovided in said furnace for preheating said combined materials to becharged, a reducing zone provided in said furnace for reducing saidmetal-containing material charged, a melting zone provided in saidfurnace for melting and reducing said metal-containing material, and acooling zone provided in said furnace for cooling said molten reducedproduct and said slag, and wherein said cooling zone is disposed in saidfurnace between said charging device and said discharging device,wherein said charging device is positioned and operative to deposit uponsaid hearth a layer of a solid-reducing material which substantiallycovers said hearth, and to deposit upon said layer an upper deposit ofsaid metal-containing material, thereby preventing direct contactbetween said hearth and the molten metal generated by said heating ofsaid metal-containing material, comprising apparatus for pressing aroller having convex portions down on the surface of said solid-reducingmaterial layer.